A new selective medium for the culture of clostridia from human faeces.

A new selective medium, sulphite-polymixin-milk (SPM) agar, for the isolation of clostridia from faeces is described. This medium contains whole cow's milk, which favours the growth of clostridia over that of Bacteroides and Bifidobacterium spp., and only small amounts of colistin (10 micrograms/ml) for suppressing growth of coliforms. The alkaline end-products of clostridia give rise to yellow colonies on a red background which are easy to distinguish from the red colonies of other not completely inhibited bacteria. The medium is suitable for isolation of many clostridia species. Comparisons were made between SPM and several other media for recovery of clostridia. The detection limit on SPM agar was more than 10(3) below that on Reinforced Clostridia Agar (Oxoid CM101).